The objective of this proposal is to examine genetic and psychosocial influences on physiological and biochemical aspects of blood pressure control in normal and hypertensive adolescents and in primary and secondary hypertensive patients, to determine which, if any of these factors may constitute precursors of hypertension in man. The principal methods involved in this investigation will involve standardized stress maneuvers, standardized physiological and biochemical maneuvers and detailed psychosociological interviews. Populations to be studied will include normotensive and hypertensive adolescent males of both black and white races, college age twins, and patients and their families with essential and secondary types of hypertension. These families with essential hypertension will be selected to include a balanced number of probands with low, normal and high renin categories. Emphasis will be placed on adolescent offspring of hypertensive patients. The psychophysiological parameters to be investigated are the responses of blood pressure, stroke volume, finger pulse volume, heart rate, skin temperature, and skin conductance level to standardized stress maneuvers. The biochemical responses induced by the maneuvers will be assessed by measuring changes in plasma norepinephrine, plasma renin activity and plasma cortisol. The stress protocol will include maneuvers, both active (e.g., mental arithmetic) and passive (e.g., cold pressor), known to effect cardiovascular physiology. Responses to these variables will be correlated with blood pressure levels throughout the range studied. The subjects with essential and secondary hypertension and their offspring will enable a comparison between normotensives and hypertensives and their offspring. Finally, a five-year follow-up of the offspring of hypertensive parents will determine if one or more of these factors enable the prediction of the development of hypertension in such subjects who are at high risk to develop increased blood pressure with time.